Today's Goals

Master If...Then...Else
Master Select Case
Nest conditions correctly

Key Concepts

1. If...Then...Else

Conditionals let the program act according to the situation. The basic form:

vba
If condition Then
    ' runs when the condition is true
Else
    ' runs when the condition is false
End If

Chain extra tests with ElseIf, and combine conditions with And and Or. Branch order decides the result: VBA tests top-down and exits at the first match, so range checks must run from high to low — otherwise 85 hits score >= 60 first and reads "Pass".

2. Select Case

One variable checked against several fixed values reads cleaner as Select Case than as a long ElseIf chain:

vba
Select Case variable
    Case value1
        ' handle value1
    Case value2
        ' handle value2
    Case Else
        ' everything else
End Select

Case supports ranges: Case Is >= 90, Case 1 To 10. Rule of thumb: Select Case for discrete values (grades, departments), If...ElseIf for ranges and combined conditions.

3. Nested Conditions

An If inside another If expresses "A first, then B" (the .bas example checks age, then student status). Past two levels, flatten the logic with And.

Today's Code

vba
Sub If示例()
    Dim score As Integer
    score = 85

    If score >= 90 Then
        MsgBox "优秀"
    ElseIf score >= 80 Then
        MsgBox "良好"
    ElseIf score >= 60 Then
        MsgBox "及格"
    Else
        MsgBox "不及格"
    End If
End Sub

Sub SelectCase示例()
    Dim grade As String
    grade = "A"

    Select Case grade
        Case "A"
            MsgBox "优秀"
        Case "B"
            MsgBox "良好"
        Case "C"
            MsgBox "中等"
        Case Else
            MsgBox "未知等级"
    End Select
End Sub

In the If example, 85 lands in the score >= 80 branch; in the Select Case example, "A" hits the first Case.

Real-World Scenario

The setup: tiered commission — 3% on sales up to 100,000, 5% from 100,000 to 200,000, 8% above 200,000:

vba
Sub 计算提成()
    Dim 销售额 As Double, 提成率 As Double

    销售额 = 150000

    If 销售额 > 200000 Then
        提成率 = 0.08
    ElseIf 销售额 > 100000 Then
        提成率 = 0.05
    Else
        提成率 = 0.03
    End If

    MsgBox "提成: " & 销售额 * 提成率 & " 元"
End Sub

150,000 takes the second branch and pops up "提成: 7500 元". Conditions must run largest-first, or deals over 200,000 stop at 5% — no error, just money quietly lost every month.

Exercises

Assign a letter grade from a score
Decide whether a given year is a leap year
Suggest a reward or penalty based on a score

Exercise Solutions

Test the score ranges with If...ElseIf or Select Case (90 and above Excellent, 80–89 Good, and so on); feed score from an InputBox return value to make it interactive.
Leap-year test: (Year Mod 4 = 0 And Year Mod 100 <> 0) Or (Year Mod 400 = 0) — Mod gives the remainder, an If reports the result.
Replace each branch's MsgBox text with a reward (dinner with friends) or a penalty (extra review).

Extension Exercises

Rewrite the If example as a Select Case version using Case Is >= 90 range syntax.
Print the largest of three numbers using only If.

Common Errors and Troubleshooting

Error / Symptom	Cause	Fix
`Compile error: Block If without End If`	A multi-line If missing End If, or ElseIf written as "Else If"	One End If per block If
Comparisons always fall through to Case Else	Leading/trailing spaces, so "A " ≠ "A"	`Trim()` before comparing
An 85 gets graded "Pass"	A broad condition ahead of narrower ones	Order range checks from high to low

Summary

If...ElseIf for ranges and combined conditions; Select Case for one variable with fixed values. Ship only after checking End If pairs and branch order.

由在线工具箱(www.vba.net)整理制作

🌱 Day03 - Conditional Statements